The present invention relates to a tire intended to be mounted on a rim having at least one first frustoconical seat, the generatrix of which has an axially outer end which is closer to the axis of rotation than the axially inner end.
Such a tire is described in U.S. Pat. No. 5,785,781. It comprises at least one first bead, which is intended to be mounted on said first rim seat which is inclined towards the outside, said first bead, of conventional axial width, which ends axially to the outside in a bead toe, having a bead seat, the generatrix of which has its axially outer end closer to the axis of rotation than its axially inner end, said generatrix being extended axially to the outside by an outer face defining the bead toe, said face forming with the axis of rotation an angle xcex3, which is open radially and axially towards the outside, of less than 90xc2x0. The radial carcass reinforcement of said tire, which is anchored within each bead to at least one inextensible annular reinforcement element, has a meridian profile, when the tire is mounted on its operating rim and inflated to its operating pressure, with a direction of curvature which is constant in the sidewalls and bead which ends in the toe and which is such that, in said bead, the tangent to the point of tangency of said profile with the inextensible annular element of said bead forms with the axis of rotation an angle xc3x8 of at least 70xc2x0 which is open towards the outside.
The bead of such a tire, and more particularly the structure of the hooking of the carcass reinforcement, may be variable. In U.S. Pat. No. 5,971,047, the radial carcass reinforcement is anchored to the inextensible element by winding around said element from the heel to the toe of the bead to form an upturn extending into a profiled element of rubber mix in the form of a wedge defined by two sides starting from an apex A located beneath the section of the coated bead wire, the radially outer side forming, with a straight line parallel to the axis of rotation passing through said apex A, an acute angle xc3x81 of between 20xc2x0 and 70xc2x0, which is open radially and axially towards the outside, and the radially inner side forming with said parallel line an acute angle xc3x82 of between 0xc2x0 and 30xc2x0, which is open radially towards the inside, and the rubber mix forming the profiled element, axially adjacent the bead wire, having a Shore A hardness equal to at least 65 and greater than the Shore A hardness(es) of the rubber mixes axially and radially above the bead wire and the profiled element.
The combination of the meridian profile of the carcass reinforcement as described in the first above-identified patent with a hooking structure as described in the second above-identified patent makes it possible to obtain a very good compromise, firstly between the properties of on-road behavior of the tire inflated to its recommended pressure, and secondly between said properties when it is inflated at reduced or even zero pressure, the beads of said tire remaining perfectly in place when travelling in degraded mode owing to their above-described structure, which structure permits modification (increase) of the clamping of the bead toe on the mounting rim as a function of the tension of the carcass reinforcement, which makes it possible to have initial clamping on rim of low value, given that said clamping will increase when the tire is inflated to its recommended pressure.
The preferred solution described in U.S. Pat. No. 5,971,047 is such that the carcass reinforcement upturn has a length such that it is in contact with the total perimeter of the profiled element or wedge; it thus forms the two, radially outer and inner, sides of the rubber profiled element and the side opposite the apex or center of said profiled element, and the end thereof is located axially beyond the point of intersection of the two, outer and inner, sides. The part of the upturn immediately adjacent the part which is wound about the bead wire can form firstly the radially outer side of the profiled element or wedge and then the side opposite the apex of said profiled element, then finally the radially inner side of said profiled element, ending beyond the junction point of the two, outer and inner, sides. It may also first form the radially inner side of the profiled element or wedge, then the side opposite the apex of said profiled element, then finally the radially outer side of said profiled element, ending in the same manner as previously.
The above two structures are complicated and difficult to implement industrially, and are therefore expensive. Furthermore, under extremely severe loading conditions, the pressure exerted by the toe of the bead on the axially outer protrusion of the rim and the high temperature which said bead may reach are such that there may occur, at the end of its life, cracking in the rubber of the protective outer layer of the bead, which cracking is propagated along the upturn, reaching the radially inner face of the anchoring bead wire with destruction of said bead.
The object of the invention is to overcome the disadvantages above while retaining the excellent anti-unwedging or anti-unseating properties of the tire in question.
The tire having a radial carcass reinforcement, in accordance with the invention, comprises, viewed in meridian section, at least one first bead, the seat of which has a generatrix, the axially inner end of which lies on a circle of diameter greater than the diameter of the circle on which the axially outer end is located, the bead heel being axially to the inside and being reinforced by at least one inextensible, annular reinforcement element which is coated with rubber mix, while the toe of the bead is axially to the outside and comprises a profiled element of rubber mix in the form of a wedge which is defined by two sides starting from an apex A located beneath the section of the annular element, the radially outer side forming, with a straight line parallel to the axis of rotation passing through said apex A, an acute angle xc3x81, which is open radially and axially towards the outside, and the radially inner side forming with said parallel line an acute angle xc3x82, which is open radially towards the inside, the rubber mix forming the profiled element, axially adjacent to the bead wire, having a Shore A hardness greater than the Shore A hardness(es) of the rubber mixes respectively radially above said annular element and the axially adjacent profiled element. It is characterized in that the radial carcass reinforcement of said tire winds at least in the first bead around said annular element from the inside to the outside to form an upturn, the end of which is located on one hand axially to the outside of a straight line P2 perpendicular to the axis of rotation and passing through the center of gravity of the meridian section of the annular element and on the other hand axially to the inside and radially to the outside of the straight line P1 supporting the radially outer side of the profiled element axially adjacent said annular element.
The increase in the clamping of the bead toe on the mounting rim according to the tension of the carcass reinforcement will be greater if the profiled element of rubber mix in the form of a wedge and defined by the two sides starting from the apex A is reinforced by at least A that part of the upturn of the carcass reinforcement which is immediately adjacent that part of the carcass reinforcement which is wound around the annular bead reinforcement element, whether said part be in the profiled element or whether it forms at least one of its sides.
Advantageously, the radial carcass reinforcement of said tire is wound, at least in the first bead, around said annular element from the inside to the outside to form an upturn, extending along the radially inner side of the profiled element in the form of a wedge, then along the side opposite the apex A, then covering axially and radially to the outside at least in part the profiled element radially above the profiled element in the form of a wedge.
Preferably, the tire comprises a second bead, the seat of which is of the same configuration as the seat of the first bead, that is to say, a seat, the generatrix of which has an axially inner end on a circle of diameter greater than the diameter of the circle on which the axially outer end is located, or seat which is said to be inclined towards the outside.
Likewise, if xe2x80x9cdiameter of an inclined seatxe2x80x9d refers to the diameter of the circle on which is located the end of its generatrix farthest from the axis of rotation, the tire advantageously has two seats which are said to be inclined towards the outside and are of different diameters.
The meridian profile of the carcass reinforcement, when the tire is mounted on its operating rim and inflated to its operating pressure, has a direction of curvature which is constant at least in the first bead and the sidewall which extends it radially, and the tangent TTxe2x80x2 to the point of tangency T of said profile with the annular reinforcement element of said bead forms with the axis of rotation an angle xc3x8 of at least 70xc2x0 which is open towards the outside.
The invention will be better understood with reference to the drawing attached to the description, which illustrates a non-limitative example of embodiment of a tire according to the invention, and which, associated with a suitable rim, forms a high-performance tire/rim assembly.